A conventional motor stator includes a plurality of stator coils each of which is comprised of a conductive coil wound around a stator core. A resin insulator is interposed between the stator core and the conductive coil to ensure insulation therebetween. After the conductive coil is inserted on the stator core through the insulator, they are entirely covered with a molding material by molding to form a stator. The molding is performed to allow the heat generated in the conductive coil to radiate to the outside and also to prevent water or the like from entering the stator.
A manufacturing method of the stator is conducted by mounting the conductive coil fitted on the insulator onto the stator core, attaching a bus bar and others, and molding them entirely.
Here, a clearance between the insulator and the conductive coil is set to be small in order to enhance heat conduction. Therefore, during the molding for the conductive coil fitted on the insulator, the molding material could not sufficiently enter the clearance, thus leaving an air layer between the insulator and the conductive coil. Such air layer is likely to decrease the heat conduction due to poor heat conductivity of the air layer, resulting in insufficient heat radiation of the motor.
To avoid the above problems, one measure is to cover the insulator and the conductive coil by molding prior to the entirely molding.
For example, JP3659874 discloses a technique of covering a flat wire with no insulation inserted in a slot insulator with an epoxy thermosetting resin by molding and, after assembling components forming a stator, entirely covering the assembly again with an epoxy thermosetting resin by molding. More specifically, the flat wire corresponding to the conductive coil is inserted in the slot insulator corresponding to the insulator, and the combined unit is installed in a slot and then covered once with the epoxy thermosetting resin. After the components forming the stator are assembled together, the epoxy thermosetting resin is molded around the assembly to complete the stator.
As the molding material, on the other hand, a thermosetting resin containing a large amount of filler is used in order to enhance crack resistance and heat conduction.
As a material of the insulator, a thermoplastic resin is used in order to enhance productivity. In the case of using the thermoplastic resin containing a large amount of filler to reduce linear expansion coefficient to the level of a coil or a stator core and enhance heat conduction, it is likely that its fluidity decreases and also tenacity decreases, leading to occurrence of cracks in the insulator itself.